It is known that a subscriber of a GSM, GPRS or UMTS mobile telecommunications network (their “home network”) may use their mobile device when located in the coverage area of a roamed network. An agreement exists between that home network and the roamed network which allows data to be shared therebetween in order to allow appropriate routing of the calls and so that the user of the mobile device can be levied a charge in dependence upon costs incurred by both the home network and the roamed network in handling the call. A fixed communication link, typically a leased telephone line, connects the home network and the roamed network and calls between the networks are routed along this link. The use of such a communication link incurs significant costs for the home network and/or the roamed network, and these are passed on to the user of the mobile device. It is partly these costs that generally make both receiving and making calls while a mobile device is roaming considerably more expensive than other types of call.